1. Technical Field
The present invention relates generally to a shock absorber for an automotive suspension system. More particularly, the invention relates to a hydraulic shock absorber which has an improved arrangement of a rod guide for guiding reciprocating motion of a piston rod.
2. Background Art
Japanese Utility Model First Publication No. 61-82141 discloses a hydraulic shock absorber which includes a rod guide having an opening in its center through which a piston rod is reciprocally displaced. A peripheral portion of the rod guide which retains the rod guide in a cylinder assembly of the shock absorber is provide with a thick wall having high rigidity.
A rod guide for such a shock absorber is manufactured by powder molding, casting, or machining, resulting in increased weight and manufacturing costs. Additionally, the conventional rod guide has higher rigidity and thus when forces act on the piston rod from a lateral direction, pressure created at a contact point of the piston rod with the rod guide locally becomes great and causes friction between the members to be increased. This results in reduced durability.
Japanese Utility Model First Publication No. 1-94639 discloses a double-cylindered hydraulic shock absorber. This shock absorber includes a rod guide which supports a piston rod so as to allow it to reciprocate. The rod guide has a liquid communication path for allowing liquid flow in a direction from the inner cylinder to the outer (reservoir) cylinder during a piston rebounding stroke. The liquid communication path is defined by cut-out portions in a supporting section of the rod guide, engaging with an inner wall of an outer cylinder, which is made of a metal plate.
An edge of the outer cylinder is crimped so as to cover the supporting section of the rod guide to mount it in the outer cylinder such that a load caused by a bounding and/or rebounding motion of a vehicle body acts on the supporting section. The rigidity of the rod guide is insufficient against the load due to the cut-out portions for defining the communication path. Therefore, a technique for forming a liquid communication path hydraulically connecting between the inner cylinder and the reservoir chamber without reducing rigidity of the metallic supporting section of the rod guide has been sought by designers.